Liquid crystal display device

Abstract

Provided is a novel liquid crystal display device without deterioration of display quality. The liquid crystal display device includes a pixel for displaying a still image with a frame frequency of 1 Hz or lower. The pixel includes a liquid crystal element which includes a liquid crystal layer and has a cell gap of d (μm). The liquid crystal layer includes a liquid crystal composition which includes a liquid crystal material. The helical pitch of the liquid crystal material is longer than or equal to 4d μm and shorter than or equal to 8d μm. With this structure, a change in voltage applied to a pixel can be kept within an acceptable range of a deviation in gray level for displaying the same image. Thus, flickers due to a low refresh rate can be reduced, which leads to an increase in display quality.

What is claimed is: 
     
         1 . A liquid crystal display device comprising a pixel for displaying a still image with a frame frequency of 1 Hz or lower,
 wherein the pixel comprises a liquid crystal element which includes a liquid crystal layer,   wherein the liquid crystal layer comprises a liquid crystal composition which comprises a liquid crystal material, and   wherein a helical pitch of the liquid crystal material is longer than or equal to 20 μm and shorter than or equal to 40 μm.   
     
     
         2 . The liquid crystal display device according to  claim 1 ,
 wherein the helical pitch of the liquid crystal material is longer than or equal to 20 μm and shorter than or equal to 30 μm.   
     
     
         3 . The liquid crystal display device according to  claim 1 ,
 wherein the liquid crystal element is driven in a TN mode.   
     
     
         4 . The liquid crystal display device according to  claim 1 ,
 wherein the frame frequency is 0.2 Hz or lower.   
     
     
         5 . A liquid crystal display device comprising a pixel for displaying a still image with a frame frequency of 1 Hz or lower,
 wherein the pixel comprises a transistor and a liquid crystal element which includes a liquid crystal layer,   wherein the liquid crystal layer comprises a liquid crystal composition which comprises a liquid crystal material, and   wherein a helical pitch of the liquid crystal material is longer than or equal to 20 μm and shorter than or equal to 40 μm.   
     
     
         6 . The liquid crystal display device according to  claim 5 ,
 wherein the transistor comprises a semiconductor layer, and   wherein the semiconductor layer comprises an oxide semiconductor.   
     
     
         7 . The liquid crystal display device according to  claim 5 ,
 wherein the helical pitch of the liquid crystal material is longer than or equal to 20 μm and shorter than or equal to 30 μm.   
     
     
         8 . The liquid crystal display device according to  claim 5 ,
 wherein the liquid crystal element is driven in a TN mode.   
     
     
         9 . The liquid crystal display device according to  claim 5 ,
 wherein the frame frequency is 0.2 Hz or lower.   
     
     
         10 . A liquid crystal display device comprising a pixel,
 wherein the pixel has a function of being supplied with an image signal with a frame frequency of 1 Hz or lower,   wherein the pixel has a function of displaying a still image,   wherein the pixel comprises a liquid crystal element,   wherein the liquid crystal element comprises a liquid crystal layer,   wherein the liquid crystal layer comprises a region whose cell gap is d (μm),   wherein the liquid crystal layer comprises a liquid crystal material, and   wherein the liquid crystal material comprises a region whose helical pitch is longer than or equal to 4d μm and shorter than or equal to 8d μm.   
     
     
         11 . The liquid crystal display device according to  claim 10 ,
 wherein the helical pitch is longer than or equal to 4d and shorter than or equal to 6d.   
     
     
         12 . The liquid crystal display device according to  claim 10 ,
 wherein the liquid crystal element is driven in a TN mode.   
     
     
         13 . The liquid crystal display device according to  claim 10 ,
 wherein the frame frequency is 0.2 Hz or lower.   
     
     
         14 . A liquid crystal display device comprising a pixel for displaying a still image with a frame frequency of 1 Hz or lower,
 wherein the pixel comprises a transistor and a liquid crystal element which comprises a liquid crystal layer and which has a cell gap of d (μm),   wherein the liquid crystal layer includes a liquid crystal composition which comprises a liquid crystal material, and   wherein a helical pitch of the liquid crystal material is longer than or equal to 4d μm and shorter than or equal to 8d μm.   
     
     
         15 . The liquid crystal display device according to  claim 14 ,
 wherein the transistor comprises a semiconductor layer, and   wherein the semiconductor layer comprises an oxide semiconductor.   
     
     
         16 . The liquid crystal display device according to  claim 14 ,
 wherein the helical pitch is longer than or equal to 4d and shorter than or equal to 6d.   
     
     
         17 . The liquid crystal display device according to  claim 14 ,
 wherein the liquid crystal element is driven in a TN mode.   
     
     
         18 . The liquid crystal display device according to  claim 14 ,
 wherein the frame frequency is 0.2 Hz or lower.